In general, a particle beam therapy system is provided with a beam generation apparatus that generates a charged particle beam; an accelerator that is connected with the beam generation apparatus and accelerates a generated charged particle beam; a beam transport system that transports a charged particle beam that is accelerated by the accelerator so as to gain predetermined energy and then emitted; and a particle beam irradiation apparatus, disposed at the downstream side of the beam transport system, for irradiating a charged particle beam onto an irradiation subject.
As an accelerator for accelerating a charged particle beam, for example, a synchrotron is utilized. A high-frequency wave is applied to a high-frequency acceleration cavity (acceleration cavity) provided in a synchrotron; pattern operation is implemented with a deflection electromagnet, and a quadrupole magnet, and the like synchronized with the high-frequency wave; then, a charged particle beam is accelerated so as to gain predetermined energy. In this situation, because the charged particle beam is made to circulate in a single and the same orbit, the circulation frequency becomes higher in proportion to the level of acceleration of the charged particle beam. Therefore, it is required to raise the acceleration frequency of an acceleration voltage, in proportion to the level of acceleration of a charged particle beam. That is to say, it is required to synchronize the magnetic field B of the deflection electromagnet with the acceleration frequency f of the acceleration voltage.
A conventional art in Patent Document 1 discloses a charged particle accelerator in which by use of a T-clock (time clock), a pattern for a deflection electromagnet is outputted so as to operate the deflection electromagnet; a B-clock (magnetic-field clock) is created based on a magnetic-field change observed with a magnetic-field measurement instrument provided in a reference electromagnet that is operated with the pattern for a deflection electromagnet; then, by use of the B-clock, a pattern for an acceleration cavity is outputted so as to activate a high-frequency acceleration cavity. In a conventional charged particle accelerator, a T-clock and a B-clock are utilized, as described above, so that the deflection electromagnet is synchronized with the high-frequency acceleration cavity. In this operation method, the T-clock and the B-clock, i.e., two clocks are utilized; therefore, the apparatus is complex. Thus, Patent Document 1 proposes a charged particle accelerator in which by utilizing only a T-clock, the pattern for a deflection electromagnet and the pattern for an acceleration cavity are outputted, and the deflection electromagnet and the high-frequency acceleration cavity are operated.